Variable length device and method

ABSTRACT

A method for treating a fracture with a variable length nail is provided. The nail is configured for at least 5 mm of axial length change in each direction. An incision is made in proximity to a fractured bone and canal is cleared through the center of the bone. The variable length nail is inserted into the canal and a distraction shaft and a housing are secured to separate portions of the fractured bone. The incision is allowed or caused to close. An external adjustment device with at least one rotatable magnet is placed in proximity to the patient&#39;s skin. The external adjustment device is operated so that a magnetic field of the at least one rotatable magnet of the external adjustment device causes the rotatable permanent magnet of the variable length nail to rotate, causing either extension or retraction of the distraction shaft relative to the housing.

RELATED APPLICATION

This Application claims priority to U.S. Provisional Patent ApplicationNo. 61/442,658 filed on Feb. 14, 2011 and U.S. Provisional PatentApplication No. 61/472,055 filed on Apr. 5, 2011. Priority is claimedpursuant to 35 U.S.C. §119. The above-noted Patent Applications areincorporated by reference as if set forth fully herein.

FIELD OF THE INVENTION

The field of the invention generally relates to medical devices fortreating conditions involving the skeletal system and in particular bonefracture applications.

BACKGROUND

Distraction osteogenesis, also known as distraction callotasis andosteodistraction has been used successfully to lengthen long bones ofthe body. Typically, the bone, if not already fractured, is purposelyfractured by means of a corticotomy, and the two segments of bone aregradually distracted apart, which allows new bone to form in the gap. Ifthe distraction rate is too high, there is a risk of nonunion, if therate is too low, there is a risk that the two segments will completelyfuse to each other before the distraction period is complete. When thedesired length of the bone is achieved using this process, the bone isallowed to consolidate. Distraction osteogenesis applications are mainlyfocused on the growth of the femur or tibia, but may also include thehumerus, the jaw bone (micrognathia), or other bones. The reasons forlengthening or growing bones are multifold, the applications including,but not limited to: post osteosarcoma bone cancer; cosmetic lengthening(both legs-femur and/or tibia) in short stature ordwarfism/achondroplasia; lengthening of one limb to match the other(congenital, post-trauma, post-skeletal disorder, prosthetic kneejoint), non-unions.

Distraction osteogenesis using external fixators has been done for manyyears, but the external fixator can be unwieldy for the patient. It canalso be painful, and the patient is subject to the risk of pin trackinfections, joint stiffness, loss of appetite, depression, cartilagedamage and other side effects. Having the external fixator in place alsodelays the beginning of rehabilitation.

In response to the shortcomings of external fixator distraction,intramedullary distraction nails have been surgically implanted whichare contained entirely within the bone. Some are automaticallylengthened via repeated rotation of the patient's limb. This cansometimes be painful to the patient, and can often proceed in anuncontrolled fashion. This therefore makes it difficult to follow thestrict daily or weekly lengthening regime that avoids nonunion (if toofast) or early consolidation (if too slow). Lower limb distraction ratesare on the order of one millimeter per day. Other intramedullary nailshave been developed which have an implanted motor and are remotelycontrolled. The motorized intramedullary nails have an antenna whichneeds to be implanted subcutaneously, thus complicating the surgicalprocedure, and making it more invasive. These devices are thereforedesigned to be lengthened in a controlled manner, but due to theircomplexity, may not be manufacturable as an affordable product. Othershave proposed intramedullary distractors containing and implantedmagnet, which allows the distraction to be driven electromagnetically byan external stator (i.e., a large electromagnet). Because of thecomplexity and size of the external stator, this technology has not beenreduced to a simple and cost-effective device that can be taken home, toallow patients to do daily lengthenings.

Fracture of long bones is often treated with trauma nails. Theseimplants are placed intramedullary to hold the bones together. Often incases of complex fracture having an irregular break geometry or havingmultiple bone fragments, it is difficult to secure the nail so that thebone is held at the correct length. Other times it is desired to holdthe bone in a manner that apply compression. Every year in the UnitedStates, more than 90,000 tibia and femur shaft fractures are defined ascomplex. Many of these fractures are treated with trauma nails withvarying results. Some of the possible complications from the treatmentof these complex fractures include: infection, vascular injuries,non-union, neural injury, associated injuries to other bone or jointlocations and heterotopic ossification. Also included in the possiblecomplications is the possibility of unmatched bilateral bone lengths.

SUMMARY

In one embodiment, a method for treating a complex fracture with avariable length nail comprising a housing and a distraction shaft, thehousing containing a rotatable permanent magnet mechanically coupled toa lead screw, the lead screw interfacing with a nut such that rotationof the lead screw in a first direction causes the distraction shaft toaxially retract within the housing and rotation of the lead screw in asecond direction causes the distraction shaft to axially extend from thehousing, wherein the nail is configured for at least 5 mm of axiallength change in each direction. The method includes making a first holeor incision in the skin of the patient in proximity to a fractured longbone and at least partially clearing a canal through the center of thelong bone and inserting the variable length nail into the canal andsecuring the housing and distraction shaft to separate portions of thefractured long bone. The hole or incision is caused or allowed to closeand an external adjustment device is placed in proximity to thepatient's skin. The external adjustment device includes at least onerotatable magnet. The external adjustment device is operated so that amagnetic field of the at least one rotatable magnet causes the rotatablepermanent magnet of the variable length nail to rotate, causing thedistraction shaft to either retract into or extend from the housing.

In another embodiment, a variable length nail system includes a nailthat includes distraction shaft and a housing, the housing containing arotatable permanent magnet mechanically coupled to a lead screw, thelead screw interfacing with a nut such that rotation of the lead screwin a first direction causes the distraction shaft to axially retractwithin the housing and rotation of the lead screw in a second directioncauses the distraction shaft to axially extend from the housing, whereinthe nail is configured for at least 5 mm of axial length change in eachdirection. The system further includes an external adjustment devicethat has at least one rotatable magnet, wherein the rotatable permanentmagnet of the nail is configured to be rotated by a moving magneticfield of the at least one rotatable magnet of the external adjustmentdevice, and wherein rotation of the at least one rotatable magnet of theexternal adjustment device in a first rotational direction retracts thedistraction shaft into the housing and rotation of the at least onerotatable magnet of the external adjustment device in a secondrotational direction, opposite of the first rotational direction,extends the distraction shaft from the housing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates side view of an intramedullary lengthening device inplace within a bone according to one embodiment.

FIG. 2 illustrates a side view of the intramedullary lengthening deviceof FIG. 1.

FIG. 3A illustrates a cross-sectional view of the intramedullarylengthening device of FIGS. 1 and 2 taken along the line 3A-3A of FIG.2.

FIG. 3B illustrates a detailed view of the intramedullary lengtheningdevice of FIG. 3A from the area of circle 3B.

FIG. 3C illustrates a cross-sectional view of the intramedullarylengthening device of FIGS. 1 and 2 taken along the line 3C in FIG. 2.

FIG. 4A illustrates a view of several of the internal components of theintramedullary lengthening device of the prior FIGS.

FIG. 4B illustrates a lip seal configured for use in the intramedullarylengthening device of the prior FIGS.

FIG. 5 illustrates a detailed view of several internal components of thedrive mechanism of the intramedullary lengthening device of the priorfigures.

FIG. 6 illustrates a perspective view of an external adjustment device.

FIG. 7 illustrates an exploded view of the magnetic handpiece of theexternal adjustment device of FIG. 6.

FIG. 8 illustrates a cross-sectional representation of a prior artelectromagnetic external device being positioned around a patient'slower thigh.

FIG. 9 illustrates a cross-sectional representation of the externaladjustment device handpiece of FIGS. 6 and 7 being positioned on apatient's lower thigh.

FIG. 10 illustrates a sterilizable kit for use with a modularintramedullary lengthening device.

FIG. 11 illustrates a modular intramedullary lengthening deviceaccording to one embodiment.

FIG. 12 illustrates one end of the actuator of the intramedullarylengthening device of FIG. 11.

FIG. 13 illustrates an extension rod of the modular intramedullarylengthening device.

FIG. 14 illustrates a second view of the extension rod of FIG. 13.

FIG. 15 illustrates a proximal drill guide for insertion and attachmentof the modular intramedullary lengthening device.

FIG. 16 illustrates a removal tool for removal of the modularintramedullary lengthening device.

FIG. 17 illustrates a torque limiting driver for attaching the extensionrod to the actuator of the modular intramedullary device.

FIG. 18 illustrates a section of the actuator of the modularintramedullary lengthening device.

FIG. 19 illustrates a gap (G) between a magnetic handpiece and anintramedullary lengthening device.

FIG. 20 illustrates a locking screw driver for use with theintramedullary lengthening device.

FIG. 21A illustrates a locking screw for use with the intramedullarylengthening device.

FIG. 21B illustrates the locking screw of FIG. 21A taken along line21B-21B of FIG. 21A.

FIG. 22 illustrates a side view of a variable length nail.

FIG. 23 illustrates a cross-section of the variable length nail of FIG.22 taken along line 23-23′.

FIGS. 24A through 24F illustrates the several steps of implantation,compression and distraction of a variable length nail implanted in afractured femur.

FIG. 24G illustrates cyclic micromovement being applied by a variablelength nail to a fractured femur.

FIG. 24H illustrates a non-movement period between applications of thecyclic micromovement of FIG. 24G.

FIG. 25 illustrates an intramedullary rotational correction deviceaccording to one embodiment.

FIG. 26 illustrates a partial sectional view of the rotationalcorrection device of FIG. 25.

FIG. 27 illustrates a longitudinal section of FIG. 26, taken along theline 27-27′.

FIG. 28 illustrates a lockable and un-lockable rotational implantaccording to another embodiment.

FIG. 29 illustrates a detailed view of region A of FIG. 28.

FIG. 30 illustrates a perspective view of an alternative interfacebetween a rotary nut and a housing of an intramedullary rotationalcorrection device like that illustrated in FIGS. 25-27.

FIG. 31 illustrates a perspective view of the interface after axial androtational translation of the rotary nut with respect to the housing.

FIG. 32 illustrates a perspective view of the rotary nut with thehousing removed for illustration purposes.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 1 illustrates the side view of an intramedullary lengthening device110 which has been placed through a hole or bore 108 contained within abone 100. The hole or bore 108 may be made by drilling, reaming and thelike and may extend through both cortical bone (at the end) and throughcancellous (spongy) bone. The intramedullary lengthening device 110illustrated in FIG. 1 includes a housing 112 and a distraction shaft114. In order to grow or lengthen the bone 100, the bone 100 either hasa pre-existing separation 106 or is purposely cut or broken to createthis separation 106, dividing the bone into a first section 102 and asecond section 104. The cut may be done prior to inserting and securingthe intramedullary lengthening device 110, or may be done after thedevice 110 is inserted, for example by use of a flexible Gigli saw. Thedistraction shaft 114 of the intramedullary lengthening device 110 isattached to the first section 102 using one or more attachment fasteners118 such as screws. Fasteners 118 other than screws known to thoseskilled in the art may also be used to secure the distraction shaft 114to the first section 102 of the bone 100. The housing 112 of theintramedullary lengthening device 110 is secured to the second section104 of bone 100 using one or more attachment fasteners 116 such asscrews. Again, fasteners 116 other than screws may be used to secure thehousing 112 to the second section 104 of bone 100.

Over the treatment period, the bone 100 is regularly distracted,creating a new separation 106, into which osteogenesis can occur.Regularly distracted is meant to indicate that distraction occurs on aregular or periodic basis which may be on the order of every day orevery few days. An exemplary distraction rate is one millimeter per dayalthough other distraction rates may be employed. That is to say, atypical distraction regimen may include a daily increase in the lengthof the intramedullary lengthening device 110 by about one millimeter.This may be done, for example, by four lengthening periods per day, eachhaving 0.25 mm of lengthening. The intramedullary lengthening device110, as disclosed in more detail below, has a magnetic drive system,which allows the distraction shaft 114 to be telescopically extendedfrom the housing 112, thus forcing the first section 102 and the secondsection 104 of the bone 100 apart from one another. As the distractionprocess is performed, a portion of the housing 112 is able to slidewithin the hole or bore 108 of the first section 102 if the housing 112is located within a displacement section 120 as illustrated in FIG. 1.Alternatively, if the housing 112 is completely contained in secondsection 104 then there is no sliding of the housing 112 relative to thehole or bore 108. The orientation of the intramedullary lengtheningdevice 110 within the bone 100 may be opposite of that shown in FIG. 1.For example, the distraction shaft 114 may be coupled to the secondsection 104 of the bone 100 and the housing 112 may be coupled to thefirst section 102 of the bone 100. For example, the intramedullarylengthening device 110 may be placed retrograde, from a hole or borestarting at the distal end of the bone 100.

Turning to FIGS. 2 through 5, the intramedullary lengthening device 110has one or more apertures 122 in the distraction shaft 114 through whichthe fasteners 118 may be placed. Likewise, the housing 112 is attachedto or otherwise integrated with an end cap 130 which has one or moreapertures 124 through which the fasteners 116 may be placed. The housing112 of the intramedullary lengthening device 110 includes a magnethousing 128 and a splined housing 126. These housings 126, 128 may beattached to each other by means of welding, adhesive bonding or otherjoining techniques. The magnet housing 128 is sealably closed at one end(the end opposite the interface with the splined housing 126) by theattachment of the end cap 130. The end cap 130 may be attached to themagnet housing 128 by means of welding, adhesive bonding or otherjoining techniques. In use, the distraction shaft 114 is driven from thehousing 112 by means of a lead screw 136 which turns inside a nut 140that is secured to an inner surface adjacent to a cavity 137 of thedistraction shaft 114. The lead screw 136 is mechanically coupled, in anindirect manner, to cylindrical permanent magnet 134 contained withinthe magnet housing 128. As explained in more detail below, rotation ofthe cylindrical permanent magnet 134, which is magnetically driven by anexternal adjustment device 180 as illustrated in FIG. 6, effectuatesrotation of the lead screw 136. Rotation of the lead screw 136 thentranslates into axial movement of the distraction shaft 114 relative tothe housing 128.

Cylindrical magnet 134 is fixedly contained within a magnet casing 158using, for example, an adhesive such as an epoxy. The magnet casing 158and cylindrical magnet 134 contained therein rotate relative to thestationary magnet housing 128. The cylindrical magnet 134 may be a rareearth magnet such as Nd—Fe—B and may be coated with Parylene or otherprotective coatings in addition to being protected within the magnetcasing 158, for example hermetically potted with epoxy. The magnetcasing 158 contains an axle 160 on one end thereof which attaches to theinterior of a radial bearing 132. The outer diameter of the radialbearing 132 is secured to the interior of the end cap 130. Thisarrangement allows the cylindrical magnet 134 to rotate with minimaltorsional resistance. At its other, opposing end, the magnet housing 158includes an axle 161, which is mechanically coupled to a first planetarygear set 154. The axle 161 includes the sun gear of the first planetarygear set 154, the sun gear turning the planetary gears of the firstplanetary gear set 154. The first planetary gear set 154 serves toreduce the rotational speed and increase the resultant torque deliveryfrom the cylindrical magnet 134 to the lead screw 136. A secondplanetary gear set 156 is also illustrated mechanically interposedbetween the first planetary gear set 154 and the lead screw 136, forfurther speed reduction and torque augmentation. The number of planetarygear sets and/or the number of teeth in the gears may be adjusted, inorder to achieve the desired speed and torque delivery. For example, alead screw 136 with eighty (80) threads per inch attached to twoplanetary gear sets of 4:1 gear ratio each inside a 9 mm device withmagnet location in the distal femur can achieve at least 100 lb. ofdistraction force at a greater than average distance or gap from theexternal device (FIG. 9 or FIG. 19). The planetary gear sets 154, 156output to a planetary gear output shaft 144. The planetary gear outputshaft 144 extends through a thrust bearing 138 and is secured (bywelding and the like) to a lead screw coupling cap 146. The lead screw136 is secured to the lead screw coupling cap 146 by a locking pin 142,which extends transversely through a hole in the lead screw 136 andcorresponding holes in the lead screw coupling cap 146. A cylindricallocking pin retainer 148 surrounds the locking pin 142, holding thisassembly together. Attaching the lead screw 136 to the rest of themagnet/gear assembly in this manner, assures that the design is notover-constrained, and thus that the lead screw 136 does not gall withthe nut 140. In addition, biocompatible grease, for example KRYTOX, maybe used on the moving parts (lead screw, nut, bearings, housing, anddistraction shaft) in order to minimize frictional losses. The leadscrew 136 is able to freely rotate within a cavity 137 of thedistraction shaft 114 and thus only needs to engage with the shortlength of the nut 140. This feature advantageously minimizes frictionallosses.

The thrust bearing 138 serves to protect the magnet/gear assembly of thedrive from any significant compressive or tensile stresses. The thrustbearing 138 consists of two separate races with ball bearings betweenthe two races. When there is a compressive force on the device, forexample, when distracting a bone 100, and thus resisting the tensilestrength of the soft tissues, the thrust bearing 138 abuts against amagnet housing abutment or lip 150 located in the magnet housing 128.Additionally, though the device is not typically intended for pullingbones together, there may be some applications where this is desired.For example, in certain compressive nail applications it is the goal tohold two fractured sections of a bone together. Because the bone 100 mayhave fractured in a non-uniform or shattered pattern, it may bedifficult to determine the desired length of the nail until after it isimplanted and fully attached. In these situations, it can be easy tomisjudge the length, and so a gap may exist between the separatesections or fragments of bone 100. By placing a slightly extendedintramedullary device 110 and securing it, the device 110 may beretracted magnetically, after it has been secured within the bonefragments, so that it applies the desired compression between the twofragments. In these compressive nail applications, there would betensile force on the device 110 and the thrust bearing 138 would abutagainst a splined housing abutment or lip 152. In both situations, thethrust bearing 138 and a rigid portion of one of the housing sections(e.g., lips 150, 152) take the large stresses, not the magnet/gearassembly of the drive system. In particular, the thrust bearing 138 issandwiched between the abutment or lip 150 and the abutment or lip 152.

Turning specifically to FIGS. 4A and 5, the housing components have beenremoved to reveal various internal features, including a lip seal flange168 and linear ball cage 162 that allows sliding of the distractionshaft 114 within the housing 112, and which also keeps the distractionshaft 114 from being able to rotate within the housing 112. This allowsfull stability of the bone 100. Distraction shaft 114 contains severalaxial grooves 166 as best seen in FIG. 3C and FIG. 4A. The grooves 166have semi-circular indentation cross-sections which allow several balls164 to roll within them. The balls 164 are trapped within the linearball cage 162. The splined housing 126 which fits over the balls 164 andlinear ball cage 162 has axial grooves 163 (FIG. 3C) along its innerdiameter surface that are similar to the axial grooves 166 of thedistraction shaft 114. In this regard, the balls 164 and the ball cage162 are interposed between the distraction shaft 114 and the splinedhousing 126. Therefore, the balls 164 are held in place by the linearball cage 162, and mechanically lock the respective grooves to eachother, thus impeding rotation of the distraction shaft 114 within thehousing 112. However, the balls 164 are able to roll within the linearball cage 162, thus allowing axial displacement of the distraction shaft114 in relation to the splined housing 126 of the housing 112 with verylow friction. The lip seal flange 168 as seen in FIG. 4A contains a lipseal 169 as seen in FIG. 4B which allows a sliding seal between thedistraction shaft 114 and the splined housing 126, thus protecting theinner contents of the entire assembly from the external (e.g., body)environment. The lip seal 169 includes a base portion 173, which sealsagainst the inner diameter of the lip seal flange 168 (and thus thesplined housing 126 which is attached to the lip seal flange 168). Thelip seal 169 also includes protrusions 171 which slidingly seal againstthe axial grooves 166 of the distraction shaft 114. Inner surface 175 ofthe lip seal 169 slidingly seals against the overall outer diameter ofthe distraction shaft 114. It should also be noted that the lip seal 169may be made from silicone, EPDM or other rubber materials, and may becoated with silicone oil, to aid in lubricity. Also, the balls, groovesand ball cage may be coated with silicone oil or a liquid perfluorinatedpolyether such as KRYTOX to aid in lubricity. FIG. 5 shows a portion ofthe magnet casing 158 removed so that the South pole 170 and North pole172 of the cylindrical magnet 134 may be illustrated.

FIG. 6 illustrates an external adjustment device 180 which is used tonon-invasively distract the intramedullary lengthening device 110 bymeans of a magnetic coupling which transmits torque. The externaladjustment device 180 comprises a magnetic handpiece 178, a control box176 and a power supply 174. The control box 176 includes a control panel182 having one or more controls (buttons, switches or tactile, motion,audio or light sensors) and a display 184. The display 184 may bevisual, auditory, tactile, the like or some combination of theaforementioned features. The external adjustment device 180 may containsoftware which allows programming by the physician. For example, thephysician may desire that the patient take home the external adjustmentdevice 180 in order that the patient or member of the patient's familyor friends make daily distractions of the intramedullary lengtheningdevice 110 implanted in the patient. However, the physician is able tokeep the person operating the external adjustment device 180 from overdistracting the patient by programming this into the control box 176.For example, the physician may pre-program the control 176 box so thatonly one (1) mm of distraction is allowed per day. The physician mayadditionally pre-program the control box 176 so that no more than 0.5 mmmay be distracted during any two hour period, or that no more than 0.25mm may be retracted during a five minute period. Settings such as thesemay serve to assure that the patient not be capable of causing severedamage to the bone or tissue, nor disrupt the lengthening process.

Preferably, such instructions or limits may be pre-programmed by thephysician or even the manufacturer in a secure fashion such that usercannot alter the pre-programmed setting(s). For example, a security codemay be used to pre-program and change the daily distraction limit (orother parameters). In this example, the person operating the externaladjustment device 180 will not be able to distract more than one (1) mmin a day (or more than two mm in a day), and will not have the securitycode to be able to change this function of the external adjustmentdevice 180. This serves as a useful lockout feature to preventaccidental over-extension of the intramedullary lengthening device 110.The safety feature may monitor, for example, rotational movement ofmagnets 186 (FIG. 7) of the external adjustment device 180, described inmore detail below, or the safety feature may monitor rotation of thecylindrical magnet 134 in the intramedullary lengthening device 110, vianon-invasive sensing means.

FIG. 7 shows an exploded view of the magnetic handpiece 178 of theexternal adjustment device 180, in order to elucidate the manner thatthe magnets 186 of the external adjustment device 180 serve to cause thecylindrical magnet 134 of the intramedullary lengthening device 110 toturn. As seen in FIG. 7, there are two (2) permanent magnets 186 thathave a cylindrical shape. The magnets 186 are made from rare earthmagnets. The magnets 186 may have the same radial two pole configurationas the cylindrical magnet 134 seen in FIG. 5. The magnets 186 are bondedor otherwise secured within magnetic cups 187. The magnetic cups 187include a shaft 198 which is attached to a first magnet gear 212 and asecond magnet gear 214, respectively. The orientation of the poles ofeach the two magnets 186 are maintained in relation to each other bymeans of the gearing system (by use of center gear 210, which mesheswith both first magnet gear 212 and second magnet gear 214). Forexample, it may be desired that the south pole of one of the magnets 186is facing up whenever the south pole of the other magnet 186 is facingdown. This arrangement, for example, maximizes the torque that can beplaced on the cylindrical magnet 134 of the intramedullary lengtheningdevice 110.

The components of the magnetic handpiece 178 are held together between amagnet plate 190 and a front plate 192. Most of the components areprotected by a cover 216. The magnets 186 rotate within a static magnetcover 188, so that the magnetic handpiece 178 may be rested directly onthe patient, while not imparting any motion to the external surfaces ofthe patient. Prior to distracting the intramedullary lengthening device110, the operator places the magnetic handpiece 178 over the patientnear the location of the cylindrical magnet 134 as seen in FIG. 9. Amagnet standoff 194 that is interposed between the two magnets 186contains a viewing window 196, to aid in the placement. For instance, amark made on the patient's skin at the appropriate location with anindelible marker may be viewed through the viewing window 196. Toperform a distraction, the operator holds the magnetic handpiece 178 byits handles 200 and depresses a distract switch 228, causing motor 202to drive in a first direction. The motor 202 has a gear box 206 whichcauses the rotational speed of an output gear 204 to be different fromthe rotational speed of the motor 202 (for example, a slower speed). Theoutput gear 204 then turns a reduction gear 208 which meshes with centergear 210, causing it to turn at a different rotational speed than thereduction gear 208. The center gear 210 meshes with both the firstmagnet gear 212 and the second magnet gear 214 turning them at a ratewhich is identical to each other. Depending on the portion of the bodywhere the magnets 186 of the external adjustment device 180 are located,it is desired that this rate be controlled, to minimize the resultinginduced current density imparted by magnets 186 and cylindrical magnet134 though the tissues and fluids of the body. For example a magnetrotational speed of 60 RPM or less is contemplated although other speedsmay be used such as 35 RPM or less. At any time, the distraction may belessened by depressing the retract switch 230. For example, if thepatient feels significant pain, or numbness in the area beinglengthened.

While the external adjustment device 180 is illustrated herein asincluding a motor 202 that is used to rotate or drive the magnets 186 inan alternative embodiment, the magnets 186 may be rotated manually. Forexample, the external adjustment device 180 may include a hand crank orthe like that can be manipulated to rotate the magnets 186. In stillanother embodiment, the external adjustment device 180 may include asingle magnet (e.g., permanent magnet) that is manually rotated about anaxis by hand. For example, the single magnet may include a hand-heldcylindrical magnet that is manually rotated by the user.

A cross section of a patient's lower thigh 218 with the intramedullarylengthening device 110 implanted within the femur 220 is shown in FIGS.8 and 9. In FIG. 9, the magnetic handpiece 178 of the externaladjustment device 180 of the invention is shown in position to adjustthe cylindrical magnet 134 of the intramedullary lengthening device 110.In FIG. 8, however, a scale depiction of a prior art magnetic stator“donut” 222 demonstrates the comparative efficiency of the two designs(FIG. 8 illustrates an intramedullary lengthening device 110 of the typedescribed herein placed in a “prior art” magnetic stator “donut” 222).Thus, the only part of FIG. 8 that is prior art refers to the magneticstator donut 222 The prior art magnetic stator “donut” 222 is large,expensive, and difficult to transport to a patient's home for dailyadjustments. In addition, the use of a circular cross-section as aone-size-fits-all device is not very efficient because of severalreasons: the cross section of most limbs is not circular, the bone isusually not centered within the limb and patients' limbs come in manydifferent sizes. In FIG. 8, the thigh has been placed through thecircular hole in the magnetic stator “donut” and the posterior portion232 of the thigh rests at the lower portion 226 of the magnetic stator“donut” 222. The strength of a magnetic field decreases in accordancewith a power (such as the inverse square) of the distance, depending onthe complexity of the specific field geometry. Therefore, in anymagnetic design, making the distance between the driving magnetic fieldand the driven magnet as small as possible is desirable. The size of thepatient's lower thigh 218 and the decision to how it is placed withinthe magnetic stator “donut” 222 in FIG. 8 create a geometry so that thedistance L₁ between the cylindrical magnet 134 and the upper portion 224of the magnetic stator “donut” 222 is about the same as the distance L₂between the cylindrical magnet 134 and the lower portion 226 of themagnetic stator “donut” 222. However, if the anterior portion 234 of thethigh were instead placed against the upper portion 224 of the magneticstator “donut” 222, the length L₁ would become less while the length L₂would become greater. Because each patient has a different sized limb,and because small limbs like the upper arm as well as large limbs suchas the upper leg are desired for treatment, the magnetic stator “donut”222 of FIG. 8 is almost impossible to optimize. Therefore, anextra-large magnetic field needs to be generated as the standardmagnetic field of the device, thus requiring more expense (for thehardware to power this larger field). This in turn means that eachpatient will be exposed to a larger magnetic field and larger tissue andfluid current density than is really required. It may be desired, insome embodiments, to maintain patient exposure to magnetic fields of 2.0Tesla or less during operation of the device. It may also be desired,according to another embodiment, to maintain patient exposure of thepatient's tissues and fluids to current densities of no more than 0.04Amperes/meters² (rms). In addition, because the intramedullarylengthening device 110 is secured to the bone 100, unnecessarily largemagnetic fields may cause unwanted motion of the bone 100, for examplein any of the radial directions of the cylindrical magnet 134. If themagnetic field is too high, the patient's leg may be moved out of idealposition, and may even cause the patient some annoyance, including pain.

The configuration of the magnetic handpiece 178 of the externaladjustment device 180 as shown in FIG. 9 optimizes the ability of themagnets 186 to deliver torque to the cylindrical magnet 134 of theintramedullary lengthening device 110, without exposing the patient tolarge magnetic fields. This also allows the cylindrical magnet 134 ofthe intramedullary lengthening device 110 to be designed as small aspossible, lowering the implant profile so that it may fit into thehumerus, or the tibia and femurs of small stature patients, such asthose who might desire cosmetic limb lengthening. As mentioned, a 9 mmdiameter intramedullary lengthening device 110 can deliver 100 lb.distraction force, and even 8 mm and 7 mm devices are possible. Thealternating orientation of the two magnets 186 (i.e., north pole of onemagnet 186 corresponding with south pole of the other magnet 186)creates an additive effect of torque delivery to cylindrical magnet 134,and thus maximizes distraction force for any specific cylindrical magnet134 size. Also, the separation (S) between the centers of the twomagnets 186 (for example 70 mm), and the resulting concave contour 238(FIGS. 6 and 7), match with the curvature of the outer surfaces of themajority of limbs, thus making the distances L₃ and L₄ between each ofthe magnets 186 and the cylindrical magnet 134 as small as possible.This is especially aided by the concave contour 238 of the magnetichandpiece 178. Also, skin and fat may be compressed by the magnet covers188 causing an indentation 236 on one or both sides which allows thedistances L₃ and L₄ between each of the magnets 186 and the cylindricalmagnet 134 to be yet smaller.

FIG. 10 illustrates a sterilizable kit 400 containing a plurality ofextension rods 406 which are configured to be attached to an actuator412 seen in FIG. 11 in order to construct a modular intramedullarylengthening device 410. In a one embodiment, the actuator 412 issupplied sterile, and the extension rods 406 and the remainder of thecontents of the sterilizable kit 400 are sterilizable by autoclave(e.g., steam), Ethylene Oxide or other methods known to those skilled inthe art. The sterilizable kit 400 contents includes one or more of theextension rods 406 and accessories 408 for use in the insertion,attachment, adjustment and removal of the modular intramedullarylengthening device 410. The contents are located within a firststerilizable tray 402 and a second sterilizable tray 404. Secondsterilizable tray 404 and first sterilizable tray 402 have a pluralityof holes 405 to allow gas to enter. Other items in the kit 400 will bedescribed in several of the following figures.

Turning to FIG. 11 the assembly of the modular intramedullarylengthening device 410 is shown. The actuator 412 is designed to beplaced in the bone of the patient in the opposite orientation than thatof the intramedullary lengthening device 110 of FIG. 1. Therefore, thedistraction shaft 413 is orientated towards the distal end of the bone(distal is the down direction in the case of FIG. 11). Distal apertures415 in the distraction shaft 413 allow the placement of distal lockingscrews 420 or other fasteners. The distal locking screws 420 (FIGS. 21Aand 21B) have proximal threads 417 for engaging the bone, while theremainder of the shaft 419 of the distal locking screws 420 is of aconstant diameter for maximum strength and stability. At the proximalend 421 of the actuator 412 there is a hexagonally-shaped male hub 414containing a transverse set screw 416, within a threaded hole 429 of thehexagonal male hub 414 (FIG. 12). The extension rod 406 (FIGS. 13 and14) has a corresponding hexagonal hole 428 or female end into which thehexagonal male hub 414 of the actuator 412 is placed. The transverse setscrew 416 is nested within the threaded hole 429 of the hexagonal malehub 414 so that it does not interfere with the hexagonal hole 428 of theextension rod 406, when they are placed together. There are two setscrew holes 422 in the wall of the extension rod 406 which are in linewith each other. The actuator 412 and extension rod 406 are placedtogether so that the set screw holes 422 extend coaxially with the setscrew 416. This allows a male hex 490 of a set screw tightening driver,such as the torque limiting driver 488 of FIGS. 10 and 17, to beinserted into a hex hole of the set screw 416. When the torque limitingdriver 488 is tightened and ratchets at its set control torque, theother end of the set screw 416, which is either threaded or anon-threaded peg, inserts into the opposite set screw hole 422, thustightly securing the actuator 412 to the extension rod 406. The setscrew holes 422 are sized to allow the male hex 490 to smoothly clear,but the non-threaded peg of the set screw 416 clear very slightly,making a static connection that cannot be easily loosened duringimplantation. If desired, bone cement may be placed in annulus of setscrew hole 422, to even further bond set screw 416. Also, a second screwmay be screwed in behind the head of the set screw into the femalethread that the set screw 416 was originally nested in. The head of thissecond screw will add additional resistance to shear failure of the setscrew 416. In addition, the second screw can be tightened so that itjams into the set screw 416, thus making back-out of the set screw 416unlikely. Any non-circular cross-section may be used in place of the hexcross-section, for example a square or oval cross-section.

Proximal locking screws 418 insert through locking screw apertures 430in the extension rod 406. The extension rod 406 may be straight, or mayhave a specific curve 432, for example, for matching the proximal end ofthe femur or tibia. It can be appreciated that the modular arrangementallows the actuator 412 to be attached to one of numerous differentmodels of extension rods 406, having different lengths, curves(including straight), diameters, hole diameters, and angulations. Thefirst sterilization tray 402 may include many of these differentextension rods 406, which may be selected as appropriate, and attachedto the actuator 412. Because the actuator 412 is supplied sterile, thisarrangement is also desirable, as only a single model need be supplied.However, if desired, several models of actuator may exist, for example,different diameters (10.5 mm, 12.0 mm, 9 mm, 7.5 mm) or with differentdistal screw aperture diameters, configurations or angulations. Thepreferred configuration for a multitude of patients and different bonetypes and sizes can be available, with a minimum number of sterileactuator models.

Turning to FIG. 15, a proximal drill guide 434 is illustrated and isconfigured for attaching to the modular intramedullary lengtheningdevice 410 to ease its insertion into the intramedullary canal, thedrilling of holes in the bone and the attachment of the proximal lockingscrews 418 to the bone. The proximal drill guide 434 comprises anextension arm 436 attached to a connection tube 446 through which alocking rod 448 is inserted. The locking rod 448 has a locking knob 450at the proximal end and a male thread 452 at the distal end. In order totemporarily attach the proximal drill guide 434 to the modularintramedullary lengthening device 410, a locking tab 454 of the proximaldrill guide 434 is inserted into a locking groove 424 of the extensionrod 406 and the locking knob 450 is turned, threading the male thread452 of the locking rod 448 into a female thread 426 of the extension rod406. Prior to the procedure a drill guide extension 438 is attached viaa knob 440 to the extension arm 436. After reaming the medullary canalof the bone to a diameter slightly larger than the outer diameter of themodular intramedullary lengthening device 410 (for example 11 mm),distal end of the modular intramedually lengthening device 410 isinserted into the medullary canal and the flat proximal surface of thelocking knob 450 is hammered with a mallet, allowing the modularintramedullary lengthening device 410 to be inserted to the correctdepth. Dimension X is sufficient to clear large thighs or hips (in theworst case femoral application). For example, 8 to 10 cm is appropriate.Once the modular intramedullary lengthening device 410 is in place inthe medullary canal, the proximal drill guide 434 is left attached and aguide sleeve 442 is placed through one of the holes 456, 458, 460, 462and slid so that the distal end 443 reaches the skin of the patient. Thedrill guide extension 438, extension arm 436 and holes 456, 458, 460,462 are dimensioned and oriented so that the guide sleeve 442 isoriented at the exact angle to allow drilling and placement of screwsthrough the locking screws holes 430 of the extension rod 406 andthrough the bone. The skin of the patient is cut and a drill bushing 444is placed through the incision, with the tapered tip 445 passing throughtissue and reaching the bone to be drilled. For example, drills andlocking screws may be inserted down the drill bushing 444, oralternatively, drills may be inserted down the drill bushing 444 andthen, after the drilling is complete, the drill bushing 444 is removedand proximal locking screw 418 is inserted down the guide sleeve 442.Alternative guide sleeves 464 and drill bushings 466 can be placedthrough holes 460 and 462, as seen in FIG. 10.

Turning to FIG. 16, a removal tool 468 is illustrated. The removal tool468 is used after the distraction period and consolidation period arecomplete. To remove the modular intramedullary lengthening device 410from the medullary canal, the skin is incised and bone exposed at thelocations of the proximal and distal locking screws 418, 420 and at theproximal end of the modular intramedullary lengthening device 410. Aremoval rod 470 is connected to the female thread 426 of the extensionrod 406 of the modular intramedullary lengthening device 410 byinserting the engagement tip 476 and screwing the male thread 474 intothe female thread 426, holding onto the locking knob 472. The lockingknob 472 contains a female thread 478 which allows the attachment of amale thread 486 of a removal extension 480, which has an impact knob 482and removal hammer 484. The male thread 486 is coupled to the removalextension 480 by a pivot 477 of a pivoting base 479. The male thread 486is secured to the female thread 478 by grasping and turning the impactknob 482. Prior to removing the modular intramedullary lengtheningdevice 410, the proximal and distal locking screws 418, 420 are removed.They may be removed with the use of the locking screw driver 498 (FIGS.10 and 20), which has a male hex tip 497 to engage the proximal ends ofthe locking screws 418, 420. A screw capture rod 500 (FIGS. 10 and 20)inserts down the center of the locking screw driver 498 and has a malethreaded tip 501. At a deeper portion past the female hex 513 in thelocking screws 418, 420 (FIGS. 21A and 21B) is a female thread 511. Themale threaded tip 501 of the screw capture rod 500 threads into thefemale thread 511 of the locking screws 418, 420, and tightened by usingthe tightening handle 503 of the screw capture rod 500 which sits at thehandle end 509 of the locking screw driver 498 so that once the lockingscrews 418,420 are removed from the bone, they are still secured to thelocking screw driver 498, and will not become prematurely displaced. Forexample, the locking screws 418, 420 will not be lost or dropped intothe patient. The modular intramedullary lengthening device 410 may nowbe removed from the medullary canal by grasping the removal hammer 484,and moving it quickly in the direction (D) so that hammer impact surface485 strikes knob impact surface 483. This is done until the modularintramedullary lengthening device 410 is completely removed. It shouldbe noted that locking knob 450 of the proximal drill guide 434 of FIG.15 also has a female thread (not pictured) so that during the insertionof the modular intramedullary lengthening device 410, if it is desiredto remove the device for any reason, the male thread 486 of the removaltool 468 may be attached to the female thread of the locking knob 450,and the removal hammer 484 can be used against the impact knob 482 toremove the modular intramedullary lengthening device 410.

The torque limiting driver 488 of FIG. 17 comprises a handle 496 and ashaft 492 having a torque-specific ratchet 494 connecting them. The malehex tip 490, fits into the hex hole of the set screw 416, or even intothe female hex 513 of the locking screws 418, 420. An exemplaryratcheting torque for the set screw 416 is 9 inch-pounds (1.0Newton-meter), and an exemplary hex size is 1/16″ (1.59 mm).

FIG. 18 illustrates the actuator 412 of FIG. 11 in a sectional view. Thedistal screw holes 415 are visible in the distraction shaft 413. Thedistraction shaft 413 is shown in a fully extended position in relationto the housing 312. The cavity 337 has opened to its maximum length. Inthis embodiment, the distraction shaft 413 has a purely cylindricalsurface, and is dynamically sealed to the housing 312 by two o-ringseals 502. The o-ring seals 502 may be made of silicone, EPDM, or otherrubber materials, and may be coated with silicone oil, to aid inlubricity. There are four axially extending grooves 326 on the innerwall of the housing 312. Tabs 504 on the end of the distraction shaft413 fit into these grooves 326 to keep the distraction shaft 413 frombeing able to rotate with respect to the housing 312. The housing 312 iswelded to a magnet housing 328 and the magnet housing 328 is welded tohexagonal male hub 414. The set screw 416 on the hexagonal male hub 414is used to attach the actuator 412 to the extension rod 406. Thecylindrical permanent magnet 334 is cased with epoxy inside magnetcasing 358 having an end pin 360. The end pin 360 inserts through radialbearing 332, allowing it to rotate with low friction. As the magnet 334is rotated by the external magnets, first planetary gear set 354, secondplanetary gear set 356 and third planetary gear set 357 allow a totalreduction of 64:1 (4×4×4). Each gear set allows a 4:1 reduction.Planetary gear output shaft 344 is attached to lead screw 336 by lockingpin 342, and locking pin 342 is held in place by cylindrical locking pinretainer 348. Thrust bearing 338 abuts housing abutment or lip 352 andmagnet housing abutment or lip 350 (thrust bearing 338 is sandwichedbetween housing abutment or lip 352 and magnet housing abutment or lip350). Therefore, thrust bearing 338 abuts housing abutment or lip 352 intension and magnet housing abutment or lip 350 in compression. It shouldbe noted that the sandwich arrangement allows for some slop or playbetween the thrust bearing 338 and the housing abutment or lip 352 andthe magnet housing abutment or lip 350. Lead screw 336 engages with nut340, which is secured within distraction shaft 413. With the 64:1 gearreduction of this embodiment, distraction forces of greater than 300pounds (1334 Newtons) have been consistently achieved with a gap (G inFIG. 19) of 2 inches (5.08 cm) between the magnetic hand piece 178 andthe intramedullary lengthening device 110. This is sufficient fordistracting a large range of typical patients.

It should be noted that although the embodiments of the intramedullarylengthening devices presented are shown to be used in a preferredorientation (distal vs. proximal), any of these embodiments may be usedwith the distraction shaft pointing distally or proximally. In addition,the invention may also be applied to distractable bone plates that arenot located within the intramedullary canal, but are external to thebone.

An alternative lengthening scheme than those presented above may be alsoused. For example, one alternative includes the purposefulover-lengthening (to further stimulate growth) followed by someretraction (to minimize pain). For instance, each of four daily 0.25 mmlengthening periods may consist of 0.35 mm of lengthening, followed by0.10 mm of retraction.

The materials of the accessories 408 are medical grade stainless steel,though other materials of varying densities may be used depending on thedesired weight and the required size. The majority of the components ofthe intramedullary lengthening devices are preferably Titanium orTitanium alloys although some of the internal components may be madefrom stainless steel.

Intramedullary placed nails are commonly used in trauma of the longbones. Most nails are secured in place with transverse locking screws,much in a similar way to that described in the intramedullarylengthening device described here. In simple fractures it is relativelyeasy for the orthopedic trauma surgeon to place standard trauma nailscorrectly, so that the resulting fixture bone is close to the samelength and configuration of the bone prior to fracture. However, incomplex fractures, it is much more difficult to visually and physically“put the puzzle pieces back together” due to the nature of the fractureand the surrounding soft tissue trauma. Complex fractures manyidentified using a commonly used classification system such as theMuller AO Classification of Fractures. In addition, to promote healing,it is often desired to place compression between the separate segmentsof bone initially, for callus formation prior to callus ossification.Also, because it may be difficult to judge the ideal fixture length ofthe bone during the initial operation, it often would be desirable toadjust the length of the nail, and thus the bone during recovery fromthe operation, when a true comparison x-ray may be taken (length of boneon treated side vs. length of bone on contralateral side). It may bedesired to take this x-ray with patient standing for an idealizedcomparison. The effect of the complex fracture may be such that acertain amount of distraction osteogenesis will be desired, to bring thefractured leg to a length that matches the other. During a lengtheningperiod, it may be identified that the quality of the fracture callus isinadequate, and that a compression should be applied for a period oftime. After this period of time, the lengthening process may berestarted, until the limb length is judged satisfactory. At this point,the nail length would be held constant until ossification is completed.

FIGS. 22, 23, and 24A-24H illustrate a variable length nail 616according to one embodiment. The variable length nail 616 is configuredfor treating complex fractures of long bones, such as the femur, tibiaand humerus. With reference to FIGS. 22 and 23, the variable length nail616 comprises a first end 618 having holes 624, 626 for accommodatinglocking screws. The variable length nail 616 also comprises a shaft 652with a second end 620 having screw holes 628, 630, 632 for accommodatinglocking screws. The variable length nail 616 also comprises a housing622 that is secured to or otherwise integrated at one thereof to firstend 618. As seen in FIG. 22 and FIG. 23, shaft 652 is telescopicallymoveable within the housing 622. The shaft 652 is thus able to extendfrom or retract into the housing 622. A dynamic seal between the housing622 and the shaft 652 is provided by two o-ring seals 634 as seen inFIG. 23. Still referring to FIG. 23, tabs 654 on the shaft 652 slidewithin grooves 636 within the housing 622. As in other embodimentsdisclosed herein, a cylindrical, permanent magnet 638 within a magnetcasing 650 is located within the housing 622 and is rotatable between athrust bearing 640 and a radial bearing 642. In this particularembodiment, there are no gear sets interposed between the cylindricalmagnet and the lead screw 646, and the location of the thrust bearing640 and the radial bearing 642 are reversed in comparison to FIG. 3A andFIG. 18, however the geared configuration and the bearing configurationsof FIGS. 3A and 18 are also possible. The non-geared configuration maybe preferred, for example, in situations that do not require largedistraction forces, and in situations where large adjustments are neededin a short amount of time. This is expected in many of the traumascenarios described. In addition, a device without the gear sets will beless expensive to manufacture. A pin 644 couples a lead screw 646 to themagnet casing 650. The lead screw 646 interfaces with a nut 648 thatresides within a hollowed portion of the shaft 652.

It should be appreciated that the variable length nail 616 is suppliedto the user neither in its most retracted (shortest) configuration norin its most distracted (longest) configuration. For example, in FIGS. 22and 23, the variable length nail 616 is depicted in the middle of itsaxial displacement. The variable length nail 616 of FIGS. 22 and 23 hasa 10.5 mm housing 622 diameter and a 65 mm total axial displacement.Generally, the variable length nail 616 is configured for at least 5 mmof axial length change in each direction, and in at least someembodiments it is configured for at least 20 mm of axial length changein each direction. It is supplied so that it is about 50% distracted(32.5 mm in the case of FIGS. 22 and 23). Alternatively, it may bedesired to supply a device that is only 10% or 25% distracted. Or amodel of device may be supplied that is 75% distraction, for example,specifically for patients who require more potential compression thanlengthening.

The variable length nail 616 is inserted by making a first hole orincision in the skin of the patient in proximity to the fractured longbone and a canal is at least partially cleared through the center of thelong bone. The variable length nail 616 is inserted into the canal andthe first and second ends 618, 620 thereof are secured to the differentportions of the fractured long bone. The different portions of thefractured long bone may be physically separate from one another prior toinsertion. Alternatively, the variable length nail 616 may be insertedinto the bone while the different portions are connected to one another.The bone may be subsequent cut using, for instance, a Gigli type wiresaw. For insertion of the variable length nail 616, the proximal drillguide 434 may be used. The locking tab 454 of the proximal drill guide434 is inserted into a locking groove 656 of the variable length nail616. Additionally, the male thread 452 of the locking rod 448 istightened into the female thread 658 of the variable length nail 616.The variable length nail 616 can be removed as described in otherembodiments using the removal tool 468.

In a complex fracture patient, the surgeon may be unsure whether astandard trauma nail will be successful at fixing the fractured bonewithout complications and will thus choose to implant the variablelength nail 616. FIG. 24A illustrates the variable length nail 616implanted in a canal 668 of a fractured femur 660. In this patient, thefracture site 662 is between the proximal end 664 and distal end 666 ofthe femur 660. The variable length nail 616 is secured to the femur 660at the proximal 664 and distal ends 666 with locking screws (not shown).After the surgery, the hole or incision is allowed to close. Afterclosure, and with the patient awake, the external adjustment device 180is placed on the thigh of the patient and operated so that the length ofthe variable length nail 616 is reduced, placing compression on thefracture site 662 as seen in FIG. 24B. This may be done, for example,the day after surgery, when the patient has recovered from anesthesia.Or it may be done a week or so after surgery, when the patient has fullyrecovered from the surgical procedure. It may also be done after severalweeks, after significant tissue healing has occurred. When the fracturecallus 670, as seen in FIG. 24C, is in the desired condition,distraction osteogenesis can be started by lengthening the variablelength nail 616 (for example 1 mm per day) with the external adjustmentdevice 180. As the distraction period progresses as seen in FIG. 24D,the bone begins to fill in between the distracted portions. At any time,it may be desired to add compression as seen in FIG. 24E at the fracturesite 662, and in this case, the external adjustment device 180 isoperated to shorten the variable length nail 616. Once again, then thefracture callus 670 is in desired condition, distraction osteogenesismay be resumed as illustrated in FIG. 24F, and may be continued untilthe target length of the femur 660 is reached.

An alternative method for using the variable length nail 616 andexternal adjustment device 180 is depicted in FIGS. 24G and 24H. Atechnique known as dynamization (also known as controlled early cyclicmicromovement) is being applied in FIG. 24G. FIG. 24H represents therest period between applications of the micromovement. Micromovement hasbeen shown with external fixation devices to enhance callus formation topromote rapid healing and return of bone strength. The user programs thecontrol box 176 of the external adjustment device 180 to cause themagnets 186 of the external adjustment device 180 to cycle in onedirection and then the other, such that the variable length nail 616 islengthened and shortened cyclically (FIG. 24G). For example, a strain of30% can be achieved by cycling from a 1.0 mm gap between bone sectionsto a 1.3 mm gap and back again, many times. For example, 500 cycles maybe desired over short periods (for example 17 minutes per day). Theperiod should be between 10 minutes per day and one hour per day, to beboth feasible in practice and worth performing. It is desirable to keepthe strain between 5% and 60%, because at these extremes, the cyclicprocess has been shown to actually inhibit healing. In between theapplications of the cyclic micromovement, the sections of bone are heldin place without movement as illustrated in FIG. 24H. It may be desiredto perform the cyclic micromovements at a relatively high rate, but arate of greater than 30 cycles per minute can be effective. It istypically desired to perform some micromovement at the fracture sitewithin the first two weeks after the injury.

Alternatively, the femur depicted in FIGS. 24A-24H could be treatedusing a retrograde placed variable length nail 616, where the device isinserted through a drilled hole which starts at the distal end of thefemur and extends proximally. The same methods can be used on tibia,humerus or even smaller bones.

In cases of complex trauma, it often occurs that the bone may heal thecorrect length, or at least close to the desired length, but that onemain bone portion may be misaligned angularly (in relation to thelongitudinal axis) in relation to another bone portion. It may bedesirable to correct this rotation of the bone using an alternativeembodiment, as depicted in FIGS. 25 through 27. This embodimentdiscloses an intramedullary rotational correction device 700 having afirst section 702 which is configured to be rotated in relation to asecond section 708. The first section 702 comprises a housing 728 and anextension rod 720 which contains holes 704, 706 for placement offasteners such as locking screws (not shown). The second section 708comprises a shaft 718 and contains holes 710, 712, 714 for placement oflocking fasteners such as screws (not shown). Depicted in FIG. 25, theextension rod 720 is attached to the housing 728 by means of set screw716, which is accessible through one or more screw holes 722. In thisassembly, a locking groove 724 is configured to engage with locking tab454 of the proximal drill guide 434 of FIG. 15. Also, a female thread726 is configured to engage with male thread 452 of the locking rod 448of the proximal drill guide 434.

The mechanism is similar in some ways to the axial distractionmechanisms of other embodiments disclosed herein, but additionalfeatures allow the rotation of a lead screw 746 to create controlledangular displacement of the second section 708 (and shaft 718) insteadof axial displacement. As seen in FIG. 26, a radially-poled cylindricalmagnet 730 and three gear sets 734, 736, 738 are held in the housing 728(which is exposed in FIG. 26) between a radial bearing 740 and a thrustbearing 742. The radial bearing 740 is held within a hollow portion 774of an end cap 762 as seen in FIG. 27, with the end cap 762 being securedto the assembly with a weld 776. The cylindrical magnet 730 is containedwithin a protective magnet casing 732 as seen in FIG. 26. Rotation ofthe cylindrical magnet 730 causes rotation of each successive gear set734, 736, 738. An external adjustment device 180 such as those describedherein (e.g., FIGS. 6 and 7) may be used rotate the cylindrical magnet730. Alternatively, a hand crank or the like can be used to rotate thecylindrical magnet 730. In still another embodiment, the externaladjustment device 180 may include a single magnet (e.g., permanentmagnet) that is manually rotated about an axis by hand to impartrotational movement to the cylindrical magnet 730.

Depicted in FIGS. 26 and 27 are three 4:1 planetary gear sets, whichcreate an overall 64:1 gear ratio. Other gear ratios and numbers ofgears sets, however, may be used. The design may also be used withoutany gear sets or with no gear sets in which case the cylindrical magnet730 drives the lead screw 746 in a one-to-one fashion. As shown in FIGS.26 and 27, the output of the third gear set 738 is coupled to the leadscrew 746 with a pin 764 which is held in place by a circumferential pinretainer 752 (FIG. 26). The lead screw 746 is engaged with an internalthread 772 of a rotary nut 744. The rotary nut 744 includes a screwengagement portion 766 and an axial sliding hex portion 768. The screwengagement portion 766 of the rotary nut 744 includes one or morenon-linear splines 748 which are configured to slide along non-lineargrooves 750 within the internal wall of the housing 728. The screwengagement portion 766 of the rotary nut 744 includes the internalthread 772 and a cavity 778 for clearance and free passage of the leadscrew 746. When an external rotating magnetic field, for example fromthe rotating magnets 186 of the magnetic handpiece 178, is applied tothe cylindrical magnet 730, the cylindrical magnet 730 is turned and viatransmission with the gear sets 734, 736, 738 turns the lead screw 746in a first direction. As the lead screw 746 is turned in this firstdirection within the internal thread 772, the rotary nut 744 extendsaxially, i.e. away from the cylindrical magnet 730. Because both thenon-linear splines 748 and the non-linear grooves 750 have matchedhelical curve shapes, the rotary nut 744 rotates slightly as it axiallyextends. For example, the non-linear spines 748 may be configured toextend around the rotary nut 744 a quarter of a turn for every 9.5 mm oflength. In concordance, the non-linear grooves 750 may be configured toextend around the interior of the wall of the housing 728 a quarter of aturn for every 9.5 mm of length. Alternatively, the non-linear grooves750 may be configured to extend a quarter turn for every 18 mm oflength. In yet another alternative, the non-linear grooves 750 may beconfigured to expand a quarter of a turn every 6 mm of length. In thisregard, the relative pitch of the non-linear grooves 570 may be adjustedto modify the degree of rotational movement. As yet another alternativeembodiment (not shown), the non-linear grooves 750 may be disposed onthe external surface of the rotary nut 744 and the non-linear splines748 may disposed on the internal wall of the housing 728.

As the rotary nut 744 axially extends and rotates, the axial sliding hexportion 768 slides inside a female hex receptacle 770 of the shaft 718.The axial sliding hex portion 768 and the female hex receptacle 770 arerotationally keyed, each having a hexagonal shape, so that when theaxial sliding hex portion 768 turns, the female hex receptacle 770 isturned with it thus turning the shaft 718. This construction allowsrelative axial sliding, namely, the shaft 718 rotates without any axialextension. The cross sectional shape may be any non-circular shape thatis conducive to keying. For example, alternatives include a square shapeor an elliptical shape. The shaft 718 is held axially on one end by aretaining collar 754 and on the other end by a lip 780, which in thisembodiment is shown integral to the shaft 718, though alternatively, itcan be made from a separate piece. An o-ring flange cap 756 is securedto the housing 728 (for example by welding or other direct bodingtechnique) and contains one or more o-ring seals 758 within one or moreo-ring flanges 760, thus sealing the internal contents of the housing728.

The intramedullary rotational correction device 700 is preferablysupplied to the customer in a sterile condition (for example by Gammairradiation), and it may be supplied to the customer in numerousconfigurations. Three specific configurations will now be described. Thesupplier may supply the device in each of these configurations, or thesupplier may supply the device in a single configuration, and the usermay adjust the device into their desired configuration. Theintramedullary rotational correction device 700 may be supplied with theinternal thread 772 positioned towards a first end 782 of the lead screw746 (near the pin 764). In this condition, the maximum amount ofclockwise rotation may be applied to the second section 708 and shaft718. Alternatively, the intramedullary rotational correction device 700may be supplied with the internal thread 772 positioned towards a secondend 784 of the lead screw 746. In this condition, the maximum amount ofcounter-clockwise rotation may be applied to the second section 708 andshaft 718. If it is not known at time of implantation, which direction arotational discrepancy is possible (or probable), it may be desired tosupply (or adjust) the intramedullary rotational correction device 700so that the internal thread 772 is positioned at an intermediate section786 of the lead screw 746. In this configuration, either clockwiserotation or counter-clockwise rotation will be available to the user.

In use, a patient is implanted with the intramedullary rotationalcorrection device 700 and locking screws are used to secure the firstsection 702 and second section 708 to the bone to be treated. If apre-existing rotational deformity is to be corrected, the implant ischosen with the correct amount of either clockwise or counter-clockwiserotation available, for example, as in the first two conditionsdescribed. If instead, the intramedullary rotational correction device700 is being used as a trauma nail, knowing that the specific type oftrauma may cause imprecise fixation, and thus a rotational discrepancy,it may be desired to have both clockwise and counter-clockwise rotationavailable. In this case, the third condition (allowing both clockwiseand counter-clockwise rotation) would be the one desired. In this thirdcondition, after the device is implanted, if the rotational discrepancyis discovered early, before consolidation of the bone fragments, thedevice may be operated as described to change the rotational orientationof the fragments gradually. If, however, the rotational discrepancy isdiscovered after the bone fragments have consolidated, an osteotomy maybe made to allow the rotation between the fragments to be imparted.

FIGS. 28 and 29 illustrate a lockable and un-lockable rotational implantdevice 800 according to another embodiment. The implant 800 has asimilar cylindrical magnet/lead screw/nut arrangement to otherembodiments described here, except the magnet 788, held between a thrustbearing 790 and a radial ball bearing 792, turns a lead screw 794,moving a nut 796, the nut 796 having teeth 810 on an axial face at theend which interlock with teeth 812 at a matching end of a rotation rod802 (as best seen in detail section in FIG. 29). The rotation rod 802 isdynamically sealed to a housing 814 by an o-ring seal 806, and heldaxially in relation to the housing 814 by a retaining collar 804. Thenut 796 has anti-rotation ears 808 to keep the nut 796 alignedrotationally with the housing 814. In particular, the anti-rotation ears808 may interface with corresponding grooves or recesses in the interiorsurface of the housing 814. If it is desired to manually change therotational orientation of two bone pieces of a patient, the magnet 788is rotated by a moving magnetic field of an external adjustment device(e.g., external adjustment device 180), so that the teeth 810 of the nut796 move away from the teeth 812 of the rotation rod 802. Then the teeth810, 812 are disengaged from each other, the limb can be grasped and onebone piece may be manually rotated with respect to the other bone piece.When the rotational orientation of the two bone pieces is as desired,the magnet 788 is turned in the opposite direction by the externaladjustment device 180, so that the teeth 810 of the nut 796 move towardsand engage with the teeth 812 of the rotation rod 802, thereby lockingthe housing 814 and the rotation rod 802 together. An optional slipclutch (not shown) located between the magnet 788 and the lead screw 794may be used to prevent binding.

FIGS. 30-32 illustrate an alternative embodiment of the interfacebetween a rotary nut 900 and a housing 902 of an intramedullaryrotational correction device like that illustrated in FIGS. 25-27. Inthe embodiment illustrated in FIGS. 26 and 27, non-linear splines 748located on the rotary nut 744 interface with corresponding grooves 750disposed along an inner surface of the housing 728. In the alternativeembodiment illustrated in FIGS. 30-32, the rotary nut 900 includes oneor more non-linear grooves 904 disposed along all or a portion of anexterior surface of the rotary nut 900. Located opposite the non-lineargrooves 904 disposed on the rotary nut 900 are corresponding non-lineargrooves 906 disposed along an interior surface of the housing 902. Forexample, both the non-linear grooves 904 disposed on the rotary nut 900and the non-linear grooves 906 disposed on the inner surface of thehousing 902 may be helical. A plurality of ball bearings 908 areinterposed between the non-linear grooves 904 of the rotary nut 900 andthe non-linear grooves 906 of the housing 902. As seen in FIG. 32, theplurality of ball bearings 908 may be held stationary by respectivecages 910. The cages 910 may include a strip of material substantiallyaligned with the non-linear grooves 904, 906 and have a plurality ofcircular pockets 912 that surround and retain individual ball bearings908. In this manner, the ball bearings 908 are held in a stationaryposition (for example, in relation to the housing 902) but allowed tospin or rotate within the non-linear grooves 904, 906. For instance, theends of the cages 910 may be clipped to the ends of the non-lineargrooves 906 disposed along the interior surface of the housing 902. Inthis embodiment, other features of the intramedullary rotationalcorrection device described with respect to FIGS. 25-27 remain the same.

While embodiments of the present invention have been shown anddescribed, various modifications may be made without departing from thescope of the present invention. As one example, the devices describedherein may be used to lengthen or reform a number of other bones such asthe mandible or the cranium. Thus, while several embodiments have beendescribed herein it should be appreciated that various aspects orelements are interchangeable with other separate embodiments. Theinvention, therefore, should not be limited, except to the followingclaims, and their equivalents.

1. A method for treating a complex fracture with a variable length nailcomprising a housing and a distraction shaft, the housing containing arotatable permanent magnet mechanically coupled to a lead screw, thelead screw interfacing with a nut such that rotation of the lead screwin a first direction causes the distraction shaft to axially retractwithin the housing and rotation of the lead screw in a second directioncauses the distraction shaft to axially extend from the housing, whereinthe nail is configured for at least 5 mm of axial length change in eachdirection, the method comprising: making a first hole or incision in theskin of the patient in proximity to a fractured long bone and at leastpartially clearing a canal through the center of the long bone;inserting the variable length nail into the canal and securing thehousing and distraction shaft to separate portions of the fractured longbone; causing or allowing the hole or incision to close; placing anexternal adjustment device in proximity to the patient's skin, theexternal adjustment device comprising at least one rotatable magnet; andoperating the external adjustment device so that a magnetic field of theat least one rotatable magnet causes the rotatable permanent magnet ofthe variable length nail to rotate, causing the distraction shaft toeither retract into or extend from the housing.
 2. The method of claim1, further comprising: operating the external adjustment device so thatthe distraction shaft retracts into the housing in order to applycompression between a plurality of sections of the fractured long bone.3. The method of claim 1, further comprising: operating the externaladjustment device so that the distraction shaft extends from the housingin order to perform a distraction of the bone and/or fracture callus. 4.The method of claim 2, further comprising: operating the externaladjustment device so that the distraction shaft extends from the housingin order to perform a distraction of the bone and/or fracture callus. 5.The method of claim 3, further comprising: operating the externaladjustment device so that the distraction shaft retracts into thehousing in order to apply compression between a plurality of sections ofthe fractured long bone.
 6. The method of claim 1, further comprising:operating the external adjustment device so that the distraction shaftand housing are cycled together and apart.
 7. The method of claim 6,wherein the total change of length during the cycling is between 5% and60% of a nominal gap between a plurality of sections of bone.
 8. Themethod of claim 7, wherein the total change of length during the cyclingis approximately 30% of the nominal gap between a plurality of sectionsof bone.
 9. The method of claim 6, wherein the distraction shaft andhousing are cycled together and apart at a frequency of at least 30cycles per minute.
 10. The method of claim 6, wherein the distractionshaft and housing are cycled together and apart for a cumulative timeperiod of greater than 5 minutes per day and less than one hour per day.11. The method of claim 10, wherein the distraction shaft and housingare cycled together and apart for a cumulative time period of greaterthan 10 minutes per day and less than 60 minutes per day.
 12. The methodof claim 1, wherein the rotation of the at least one rotatable magnet iscyclic.
 13. The method of claim 1, wherein the operating step isperformed one day after the inserting step.
 14. The method of claim 1,wherein the operating step is performed at least one week after theinsertion step.
 15. The method of claim 1, wherein the operating step isperformed after the patient has at least partially recovered from asurgical procedure associated with the insertion step.
 16. The method ofclaim 1, wherein the operating step is performed at least one week afterthe patient has at least partially recovered from a surgical procedureassociated with the insertion step.
 17. A variable length nail systemcomprising: a nail comprising a distraction shaft and a housing, thehousing containing a rotatable permanent magnet mechanically coupled toa lead screw, the lead screw interfacing with a nut such that rotationof the lead screw in a first direction causes the distraction shaft toaxially retract within the housing and rotation of the lead screw in asecond direction causes the distraction shaft to axially extend from thehousing, wherein the nail is configured for at least 5 mm of axiallength change in each direction; and an external adjustment devicecomprising at least one rotatable magnet, wherein the rotatablepermanent magnet of the nail is configured to be rotated by a movingmagnetic field of the at least one rotatable magnet of the externaladjustment device, and wherein rotation of the at least one rotatablemagnet of the external adjustment device in a first rotational directionretracts the distraction shaft into the housing and rotation of the atleast one rotatable magnet of the external adjustment device in a secondrotational direction, opposite of the first rotational direction,extends the distraction shaft from the housing.
 18. The variable lengthnail system of claim 17, wherein the nail is configured forsubstantially the same amount of axial length change in the extendingdirection as in the retracting direction.
 19. The variable length nailsystem of claim 17, wherein the nail is configured for more axial lengthchange in the retracting direction than in the extending direction. 20.The variable length nail system of claim 17, wherein the nail isconfigured for more axial length change in the extending direction thanin the retracting direction.
 21. The variable length nail system ofclaim 17, wherein the rotatable permanent magnet mechanically is coupledto a lead screw through at least one gear set.
 22. The variable lengthnail system of claim 21, further comprising a thrust bearing interposedbetween the lead screw and the at least one gear set.
 23. The variablelength nail system of claim 17, further comprising a thrust bearing anda radial bearing disposed in the housing on opposing sides of therotatable permanent magnet.
 24. The variable length nail system of claim17, wherein the nail is configured for at least 20 mm of axial lengthchange in the extending and retracting directions.
 25. The variablelength nail system of claim 24, wherein the nail is configured for atleast 32.5 mm of axial length change in the extending and retractingdirections.